linux-kernel - Re: [BUG?] ppc64le: fentry BPF not triggered after live patch (v6.14)

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Message-ID: <CAPhsuW5yBLMPJy3YNoJKUfP+BEsKOgJZ_BjrJnyUQ=tMPqC7ag@mail.gmail.com>
Date: Thu, 3 Apr 2025 11:33:09 -0700
From: Song Liu <song@...nel.org>
To: Naveen N Rao <naveen@...nel.org>
Cc: Jiri Olsa <olsajiri@...il.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Shung-Hsi Yu <shung-hsi.yu@...e.com>, Hari Bathini <hbathini@...ux.ibm.com>, bpf@...r.kernel.org, 
	Michael Ellerman <mpe@...erman.id.au>, Mark Rutland <mark.rutland@....com>, 
	Daniel Borkmann <daniel@...earbox.net>, Masahiro Yamada <masahiroy@...nel.org>, 
	Nicholas Piggin <npiggin@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, Vishal Chourasia <vishalc@...ux.ibm.com>, 
	Mahesh J Salgaonkar <mahesh@...ux.ibm.com>, Miroslav Benes <mbenes@...e.cz>, 
	Michal Suchánek <msuchanek@...e.de>, 
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, 
	linux-trace-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: [BUG?] ppc64le: fentry BPF not triggered after live patch (v6.14)

On Thu, Apr 3, 2025 at 8:30 AM Naveen N Rao <naveen@...nel.org> wrote:
[...]
>
> We haven't addressed this particular interaction in the powerpc support
> for ftrace direct and BPF trampolines. Right now, live patching takes
> priority so we call the livepatch'ed function and skip further ftrace
> direct calls.
>
> I'm curious if this works on arm64 with which we share support for
> DYNAMIC_FTRACE_WITH_CALL_OPS.

We still need to land [1] for arm64 to support livepatch. In a quick test
with [1], livepatch and bpf trampoline works together. I haven't looked
into the arm64 JIT code, so I am not sure whether all the corner cases
are properly handled.

[1] https://lore.kernel.org/live-patching/20250320171559.3423224-1-song@kernel.org/

Thanks,
Song

> > >
> > > Hmm, I'm not sure how well BPF function attachment and live patching
> > > interact. Can you see if on x86 the live patch is actually updated when a
> > > BPF program is attached?